Conveying blades for a compressible rotor

ABSTRACT

To provide a simple embodiment of a rotor for a fluid pump which is nevertheless very flexible in handling and compressible, in accordance with the invention a conveying blade is provided having at least two struts and a membrane spanned between them in the expanded state, wherein the struts each have at least one joint, in particular more than one joint, which enables an angling in a first direction in a first movement plane and bounds an overelongation beyond an elongation angle of in particular 180° in the opposite second direction. In particular when a plurality of joints are provided at the struts, they, and with them the conveying blades, are particularly flexible for simple compressibility.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/069,627, filed Mar. 14, 2016, which is a continuation of U.S.application Ser. No. 13/261,319 filed Aug. 8, 2012 (now U.S. Pat. No.9,314,558), which is a national stage filing under 35 U.S.C. § 371 ofInternational Application No. PCT/EP2010/007998, filed on Dec. 23, 2010,which claims priority to U.S. Provisional Application Ser. No.61/289,645, filed Dec. 23, 2009, and European Patent Application No.09075571.1, filed Dec. 23, 2009. The specifications of each of theforegoing applications are hereby incorporated by reference in theirentirety. International Application No. PCT/EP2010/007998 was publishedunder PCT Article 21(2) in English.

TECHNICAL FIELD

The invention is in the field of mechanical engineering, in particularmicroengineering, and relates to conveying blades for rotors of fluidpumps which are particularly suitable for use in areas which aredifficult to access.

BACKGROUND

Such pumps can be configured so small as micropumps in medicalengineering, for example, that they can be introduced into blood vesselswith microinvasiveness. They can then be used for assisting the pumpingforce of the human heart.

To make such pumps advantageously deployable, they are often designedcompressible and expandable so that they can be introduced in acompressed state through a blood vessel, for example up to and into aventricle, and can be expanded there.

Provision is often made for this purpose that a corresponding rotor ofthe pump which can be driven very fast in operation is radiallychangeable, i.e. compressible and expandable between the transport stateand the operating state.

Similar applications are, however, also conceivable in the non-medicalarea with larger pumps which should be used in regions difficult toaccess.

A plurality of such pumps are already known, with different principlesbeing used to achieve compressibility. It is known from WO 98/53864 touse an axial flow pump having a rotor, wherein the rotor has the form ofa rigid tube which is externally journalled in a stator. In thisrespect, the drive can be directly integrated into the stator and therotor as an electromagnetic drive.

A pump having a compressible rotor is, in contrast thereto, known fromWO 03/103745 A2, wherein the rotor with this pump has an unfoldablerotor blade which unfolds in operation due to the fluid pressure of theblood.

A pump is known in WO 2006/051023 having a rotor which has two coversurfaces and centrifugal blades disposed therebetween. The coversurfaces are pivotably fastened to the hub by means of joints.

BRIEF SUMMARY

It is the underlying object of the present invention with regard to theprior art to provide a rotor or a conveying blade for a rotor which arecompressible and expandable and in this respect have a constructiondesign which is as simple as possible, are reliable and durable as wellas inexpensive in manufacture.

The object is satisfied by the features of the invention in accordancewith claim 1.

In this respect, a corresponding conveying blade has at least two strutsas well as a membrane held between them in the expanded state of therotor or in the elongated state of the struts, and the struts in turneach have at least one joint, in particular more than one joint, whichallows an angling in one direction in a first movement plane and boundsan overelongation beyond an elongation angle, in particular 180°, in theopposite second direction within the first movement plane. Theelongation angle can also be less than 180°, for example 170°, 160° or180°, or more than 180°, for example 190°, 200° or 210°, if a strut isintended to be realized which is curved in the operating state. Theelongation angle of mutually adjacent joints can be equal, but can alsovary. In this respect, a further deformation beyond the elongation anglecan moreover be possible in operation by mechanical strain on the strutsby a fluid counter-pressure while utilizing the elasticity of the strutsections and the inherent elasticity of the joint material, with theforce required for a further deformation/elongation, however, risingsteeply on a reaching of the elongation angle.

The joint or joints are in this respect arranged over the length of theindividual struts and are at least partly spaced apart from the hub suchthat they separate different sections of the struts from one another andallow the mutual angling of the individual sections. The conveying bladecan thereby be easily folded or rolled up.

In this respect, at least one joint is spaced apart from a hub of therotor, for example by at least the radios or twice the radius of thehub.

All of the joints, or at least the majority of joints, areadvantageously kinkable in the same direction of movement so that thetotal conveying blade can be rolled up.

Such a joint kinkable in one direction is in particular at least furtherpivotable in this first direction than in the opposite second directionwithin the same movement plane. The movability of a joint is thusasymmetrically bounded in the two opposite directions starting from theelongated position.

In the rolled-up state, the conveying blade or the rotor to which it isfastened thus has a small radial extent and can thus easily be broughtto the operating site.

Alternatively, adjacent joints can also be able to be angled in oppositedirections to enable a concertina-like folding together. It is importantin this respect that all the joints of the struts are brought into adefined, elongated position by the fluid counter-pressure and arestabilized there. The named joints are generally advantageously, but notnecessarily, configured as flexural hinges, integral hinges or hingejoints.

After being brought to the operating site/deployment site, the rotor canbe driven so that the conveying blade or a plurality of conveying bladesare erected by centrifugal forces and/or by a fluid counter-pressurewhich is adopted.

In a modified embodiment, the unfolding of the rotor can also berealized by elastic restoring forces in the joints. The elasticrestoring forces can also become effective in combination withcentrifugal forces or fluid counter-pressure.

The active area of the conveying blade or conveying blades is thusincreased so that the corresponding fluid pump has a good efficiency inoperation.

To stabilize the respective conveying blade in expanded form in thedeployed state, provision is made that the individual joints bound anoverelongation of the strut or of the mutually adjacent sections beyondthe elongation angle. In this respect, the respective joint can also beable to be elongated elastically some degrees beyond 180°, butadvantageously no more than 200°. The conveying blade can thus, forexample, react with elastic yielding to impact strains in operation.

A plurality of joints, for example two, more than five, more than ten ormore than twenty joints, are advantageously provided at each of thestruts to facilitate a smooth rolling up, folding up or compressing ofthe conveying blades.

The different struts can be mutually connected to one another by furtherstruts which facilitate an opening of the conveying blades and can holdthe membrane spanned. These connection struts can in turn be connectedto the joints.

At least two struts, in particular also three struts, can advantageouslybe arranged parallel to one another or in fan shape starting from acommon base. An ergonomically favorable conveying blade which can befastened to a hub of a rotor can thus easily be designed from two ormore struts. The conveying blade can, for example, have the form of anairplane propeller blade overall.

The individual struts can advantageously start from a common point inthe region of the hub, expand the conveying blade radially outwardly inthe manner of a fan and, optionally, converge again radially outwardlytoward the tip of the conveying blade or be connected to one anotherthere by a transverse strut.

Provision can, however, also be made that the struts are fastened to anarc segment in the region of the hub, for example to an arc segment of acircle or to an elliptical arc segment or to a ring which is outwardlyfastened to the hub. Different arc segments of a circle of differentconveying blades can then be combined to a circular ring which caneasily be pushed onto a hub of a rotor.

Provision can moreover advantageously be made that the first movementplane which corresponds to an expanded state of the rotor in the maximumelongated state of the joints extends parallel to a common plane of thestruts or tangentially to the membrane spanned between the struts in theregion of said struts. In this case, the conveying blade can easily beflipped together or folded together or rolled up in the plane of themembrane or tangentially to the membrane surface and can be rolled uparound the hub in the compressed state of the rotor, for example in theperipheral direction.

Provision can be made alternatively to this that the first movementplane which corresponds to an expanded state of the rotor in the maximumelongated state of the struts extends substantially perpendicular to acommon plane of the struts or extends perpendicular to the membranespanned between the struts in the region of said struts. In this case,each of the conveying blades can be rolled up, flipped over or foldedperpendicular to the plane of the blade surface so that the conveyingblades can, for example, be laid against the hub parallel thereto in thelongitudinal direction to minimize the radial extent of the rotor.

The individual joints prevent a corresponding compression movement inthe respective direction opposed to the kinking so that the conveyingblades are stabilized in operation.

A folding together of the respective rotor can, for example, therebytake place or be supported in that the rotor is braked or is movedagainst the operating direction during pumping. Provision can be madethat the joints are biased such that they are only held in the elongatedstate in operation by the fluid counter-pressure or the centrifugalforce so that the rotor or the conveying blades automatically roll upwhen the rotor is stationary.

An advantageous embodiment of the invention provides that at least onejoint has a support element at which at least one section of a strut isrotatably mounted and two adjacent sections are supported in theelongated state. The respective support element can be configured, forexample, as a plate having a bearing block at which a respective sectionof a strut is mounted so that it is kinkable in a first direction withrespect to the support element or with respect to a second section ofthe strut, but can only be angled in a second movement direction up tothe elongation angle, for example, not substantially more than 180° intoan elongated position of the strut. In this respect, in dependence onthe position of the bearing block or the bearing point, the respectivesection can in each case abut the support element to bound theelongation movement either on the side of the bearing facing the secondsection or on the side of the bearing remote from the second section.

The support element can advantageously be structured symmetrically withrespect to a center plane between two sections mutually adjacent at thejoint. The support element can moreover comprise a material which ismore elastic than the material of the strut.

A further advantageous embodiment of the invention provides that a firstsection of the strut is pivotably journalled at a second section of thestrut in a bearing of a joint such that the two sections partly overlapin the longitudinal direction in the elongated position and that thefirst section has a pivot lever on a first side of the bearing and asupport lever on the other side of the bearing, with the support leverbeing supported at the second section in the elongated state of thejoint.

In the elongated state of the strut, the two mutually adjacent sectionsare approximately parallel to one another and are supported on oneanother such that the first section is mounted in a bearing fastened tothe second section and has a pivot lever on the one side of the bearingand a support lever on the oppositely disposed side of the bearing, withthe support lever being supported at the second section in the elongatedstate. In the opposite direction, the pivot lever is freely pivotableand the support lever is distanced from the point at which it issupported at the second section in the elongated state.

Alternatively to this, provision can also be made that a first sectionof the strut is mounted at a second section of the strut in the bearingof a joint such that the two sections partly overlap in the longitudinaldirection in the elongated position and that the first section has apivot lever on a first side of the bearing and a support lever on thesecond side of the bearing, with the pivot lever being supported at theend of the second section in the elongated state. In this case, thepivot lever is in turn supported at the second section and is freelymovable in the opposite direction in the elongated state.

A further advantageous embodiment of the invention provides that a firstsection of the strut and a second section of the strut are arrangedadjacent to one another at the end face in the elongated state and areconnected to one another by means of an asymmetrical film hinge.

The two sections can generally be kinked with respect to one anotherwith respect to the angle enclosed between them by the provision of afilm hinge. It is ensured by the asymmetrical design of the film hingethat the kinking is possible in a first direction, but is bounded in asecond direction in the elongated state of the strut.

Provision can specifically be made for this purpose that the film hingeis arranged at the side of the strut disposed inwardly in the compressedstate of the rotor and in the kinked state of the strut where thesections of the strut kinked with respect to one another include thesmaller angle with one another and that each of the sections forms anabutment at the outwardly disposed side of the strut, with the abutmentscontacting one another in the elongated state of the strut.

The inwardly disposed side of the strut means the side which has anangle less than 180° in the compressed state of the conveying blade. Inthis region, different mutually adjacent sections of the strut can befolded toward one another. The opposite side of the strut with respectto its longitudinal axis or longitudinal plane is called the outer side.

A corresponding film hinge can either comprise a different material thanthe sections and can be connected to both sections, for example byadhesive bonding, welding or other joining techniques, or the film hingecan comprise the same material as the sections and also be contiguousthereto in one piece.

It is, for example, possible in this case to provide the film hinge byintroduction of a cut-out at the outer side of the strut. Such a cut-outcan, for example, be introduced by laser cutting, etching or othererosion techniques. The corresponding cut-out can be introduced as astraight section or also as a wedge-shaped cut-out or in another form.The size of the cut-out determines when the two sections of the strutabut one another at the outer side disposed opposite the film hinge on amovement of the strut in the elongation direction and thus bound anoverelongation.

In another alternative of the embodiment of a joint, provision can alsobe made that the first and second sections of the strut are connected toone another at the end face by means of a joint section which comprisesa material at the inner side of the strut at least up to the centerplane of the strut which is more easily compressible than the materialon the outer side of the strut. A separate joint section is thenprovided which has a different structure on the inner side and outerside of the strut, for example is comprised of different materials. Thematerial on the inner side of the strut is advantageously easilycompressible, at least more easily compressible than on the outer sideof the strut. The material located at the outer side of the strut can bedesigned as stretchable, as hard as possible and non-compressible. Withgood compressibility, the material on the inner side of the strut (whichis therefore more compressible than on the outer side) can be configuredas highly tensile, for example can be reinforced through highly tensilefibers.

Provision can also be made that the strut is coated on the outside inthe joint region with a material which is harder than the material ofthe joint section.

The invention also relates, in addition to a conveying blade for acompressible rotor, to a rotor for a fluid pump which is provided withcorresponding conveying blades. The invention furthermore also relatesto a corresponding fluid pump, in particular to a blood pump for themedical area, which is equipped with a corresponding compressible rotoror compressible conveying blades in accordance with the invention.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be shown and subsequently described in the followingwith reference to an embodiment in a drawing. There are shown

FIG. 1 generally, the use of a blood pump in accordance with theinvention with a compressible rotor in a ventricle;

FIG. 2 schematically, the structure of a conveying blade with threestruts arranged in fan shape;

FIG. 3 the structure of a conveying blade with a base in the shape of acircle segment;

FIG. 4 a view of a rotor in expanded form;

FIG. 5 a view of the rotor of FIG. 4 in compressed form;

FIG. 6 a view of a further rotor in expanded form;

FIG. 7 a view of the rotor of FIG. 6 in compressed form;

FIG. 8 a schematic view of a joint of a strut;

FIG. 9 the joint of FIG. 8 in different states, schematically;

FIG. 10 a further joint of a strut in a first state;

FIG. 11 the joint of FIG. 10 in a second state;

FIG. 12 a joint of a strut which is provided in a joint section at whichtwo sections are arranged at the end face;

FIG. 13 a film hinge of a strut in a first state;

FIG. 14 the film hinge of FIG. 13 in a second state;

FIG. 15 a further embodiment of a film hinge; and

FIG. 16 the embodiment of a joint section at a strut.

DETAILED DESCRIPTION

FIG. 1 shows a heart pump 1 which is located at its deployment site inthe interior of a ventricle 3 and has a rotor 2 which has conveyingblades on a hub 10 and is arranged inside a pump housing 9. The pumphousing 9 is located at the transition from a blood vessel 4 to theventricle 3. The pump is able to suck blood out of the ventricle 3 andto convey it into the blood vessel 4.

The pump 1 is arranged at the end of a hollow catheter 5 which isintroduced through a sluice 8 into the body of a patient or into theblood vessel 4 and which accommodates a shaft 6 in its interior whichcan be driven at high speeds and is connected to the hub 10 within thepump. The shaft 6 is connected to a motor 7 at its proximal end at thedrive side.

To transport the pump 1 through the blood vessel, it can be radiallycompressed in order then to be radially expanded after being broughtinto the ventricle 3 and to achieve a correspondingly improvedefficiency or the desired pump performance.

FIG. 2 shows by way of example a conveying blade 11 of the rotor 2 inaccordance with the invention in which a membrane is spanned betweenthree struts 12, 13, 14 and is fastened to the individual struts, forexample, by means of adhesive bonding, welding or in a similar manner.

The membrane can also be attached simply by dipping the struts into aliquid plastic, for example polyurethane. The struts 12, 13, 14 eachhave a plurality of joints 15, 16, 17 of which three or four arerespectively shown at the individual struts.

The struts 12, 13, 14 converge at their base at a point 37 in which theyare fastened to a hub 10.

The nature of the joints 15, 16, 17 will be looked at in more detailfurther below.

FIG. 3 shows a modified construction of a conveying blade 11′ withstruts 12′, 13′, 14′ which each have joints 15′, 16′, 17′ and whichconverge at a base 37′ which is configured in the form of a segment ofan arc of a circle and can be fastened to a correspondingly formed hub10 of a rotor.

The movement plane which is aligned within the plane of the struts 12′,13′, 14′ or tangentially to the membrane at the respective point isshown by the arrows 38, 39 in FIG. 3.

The directions perpendicular to the corresponding plane of the membraneor of the tangential surface of the membrane at the respective point areindicated by the arrows 40, 41.

FIG. 4 shows two conveying blades of which the upper one is marked by11″ and is shown in more detail. The two conveying blades are fastenedradially opposite to one another, symmetrically at a hub 10. Theconveying blade 11″ has struts 12″, 13″ between which a membrane isspanned, with each of the struts as well as a third strut 14″ disposedbetween them having joints 15″, 16″, 17″ which are kinkable in the planeperpendicular to the surface of the conveying blade 11″ or at therespective struts perpendicular to the membrane surface or to thetangent of the membrane surface.

In this way, the individual conveying blades 11″ can be folded onto thehub 10 in the axial direction thereof as is shown in FIG. 5 in thecompressed state of the rotor with reference to the struts 12″ and 13″.

The struts 12″, 13′ are radially erected in operation by centrifugalforces by rotation of the hub, driven by the shaft 6 shown in FIG. 1.

FIG. 6 shows a further rotor having two conveying blades of which theupper one is marked by 11′″. It has struts 12′″, 13′″, 14′″ which areprovided with respective joints 15′″, 16′″, 17′″. The joints are eachkinkable in a first movement direction within the plane of the conveyingblade, i.e. parallel to the membrane in the region of the respectivestrut or to a tangential surface of the membrane so that the conveyingblades 11′″ can be flipped or folded onto the hub 10 in the peripheraldirection.

In the compressed state, the struts 12′″, 13′″ lie about the hub 10, asis shown in more detail in FIG. 7.

FIG. 8 shows the construction of the joints in a first embodiment inmore detail, with a support element 20 being shown in the form of aplate between two sections 18, 19 of a strut. The support element 20 hastwo bearing blocks 21, 22 which are shown in more detail in a side viewin FIG. 9 and in which a respective bearing shaft 21′, 22′ isjournalled. The sections 19, 19 are rotatably journalled on thecorresponding shafts.

The section 19 is additionally shown by dashed lines in theoverelongated position 19′ on the right hand side of the support element20 and the second is supported at this position at the point marked by43 at the support element 20, whereby a further angling of the section19 with respect to the section 18 is prevented.

The section 19 on the right hand side is marked by 19″ in the kinkedposition which is likewise shown by dashed lines. The correspondingstrut is angled or folded with the sections 18, 19 in this kinkedposition so that the rotor adopts a compressed position.

Only the angled position of section 18 is shown by 18″ at the left handside.

FIG. 10 represents a further embodiment of the invention in which asupport element has been omitted, the two sections 41, 42 partly coverone another in the elongated position in the longitudinal direction,with the section 42 having a pivot lever 43 and a support lever 44 atboth sides of the bearing point 23 and with the pivot lever 43projecting beyond the other section 41 and being able to be angled.

In FIG. 11, the arrangement is shown with the two sections 41, 42 in amaximally elongated position, with the section 42′ pivoted with respectto FIG. 10 being shown in the maximally overelongated position. Thesupport lever 44 is supported against the section 41 in this position. Afurther overelongation of the strut which has the two sections 41, 42 isthus prevented.

It is important for such an embodiment of a joint that the longitudinalaxis 24, 25 or the pivot planes of the two sections 42, 41 are locatedin the same plane or in parallel planes which are only minimally offsetwith respect to one another.

In FIG. 12, a strut having two sections 27, 28 which are connected toone another by a joint section 29 is shown schematically.

FIG. 13 shows in more specific form a cut-out 30 in the form of a slitor incision which is introduced into the strut between the sections 27′,28′.

FIG. 14 shows the strut of FIG. 13 in a kinked arrangement of thesections 27′, 28′, with the film hinge 31 lying on the inner side of thestrut and the cut-out 30 on its outer side. The sections 27′, 28′ thusinclude a smaller angle on the inner side than on the outer side whenthe strut is angled.

In the elongated state of the strut, the sections on the inner side havean angle which amounts to a maximum of 180°, or only a little above it,for example to a maximum of 190°.

In FIG. 15, another form of the cut-out 32 is shown which does notfollow a straight cut, but rather a more complicated shape and whichthus provide a longer and more flexible film hinge. Such a complexcut-out 32 can be introduced, for example, by means of laser cutting oretching techniques or other erosive processing techniques.

FIG. 16 represents another alternative in the formation of a joint at astrut. In FIG. 16, the joint section between two sections 27′″ and 28′″is marked by 33. This joint section 32 has a material 34 on the innerside which can also extend over the center plane 45 of the correspondingstrut up to the outer side of the strut which extends perpendicular tothe plane of the drawing.

A layer 35 is advantageously provided at the outer side of the strut,said layer being harder than the material 34 and above all beingincompressible so that the strut cannot be angled toward the outer sideand the overelongation of the strut is already prevented by the propertyof the material of the part 35. The material 34 is advantageously easilycompressible, but solid.

In addition, a layer 36 is shown in FIG. 16 which can likewise beattached to the outer side of the strut instead of the layer 35, oradditionally thereto, but is stretchable just like the material of thelayer 35 so that, on the one hand, a kinking of the sections 27′″, 28′″toward the inner side of the strut is allowed, a kinking of the sectionstoward the outer side is, however, limited.

A simple compressibility of a rotor for a fluid pump is achieved by thedesign in accordance with the invention of conveying blades or of arotor for a fluid pump having the corresponding joints so that theconveying blades can be brought into the compressed state completelywithout counter-forces or with small elastic counter-forces and can alsobe erected again after being brought to the operating site. Thedescribed joints are of simple design, are simple to manufacture and arereliable and give the corresponding conveying blades a high flexibility.

1. A catheter comprising: a distal end and a proximal end; a rotordisposed at the distal end of the catheter, the rotor comprising a huband a conveying blade; the conveying blade comprising a membrane heldbetween and attached to at least two struts; wherein at least one strutcomprises a first section and a second section and at least oneasymmetric film hinge formed in the strut, the asymmetric film hingeinterposed between and connecting the first section of the at least onestrut and the second section of the at least one strut, wherein theasymmetric film hinge is configured such that the first section of theat least one strut kinks with respect to the second section of the atleast one strut in a first direction but is bounded from kinking in asecond direction when the strut achieves a stabilized elongated positionwhen the rotor is in operation.
 2. The catheter of claim 1, whereincutout is biased so that the conveying blade is held in the stabilizedelongated position when the rotor or the conveying blade are subjectedto centrifugal force.
 3. The catheter of claim 1, wherein the asymmetricfilm hinge is arranged at a side of the at least one strut disposedinwardly in a compressed state of the rotor wherein the first section ofthe at least one strut is kinked with respect to the second section ofthe at least one strut wherein the sections of the at least one strutthat are kinked with respect to one another form an angle less than 180degrees.
 4. The catheter of claim 3 wherein an angle between respectiveouter sides of the first section of the at least one strut and thesecond section of the at least one strut when the blade achieves thestabilized elongated position when the rotor is in operation is about160 degrees to about 210 degrees.
 5. The catheter of claim 3 wherein theasymmetric film hinge comprises a cut-out formed in the at least onestrut between the first section of the at least one strut and the secondsection of the at least one strut.
 6. The catheter of claim 5 whereinabutments oppositely disposed on either side of the cut-out prevent thefirst section of the at least one strut from substantially kinking withrespect to the second section of the at least one strut when the bladeachieves the stabilized elongated position when the rotor is inoperation.
 7. The catheter of claim 1 wherein the asymmetric film hingeis made of the same material as the first section of the at least onestrut and the second section of the at least one strut.
 8. The catheterof claim 7 wherein the asymmetric film hinge is a cut-out formed betweenthe first section of the at least one strut and the second section ofthe at least one strut.
 9. The catheter of claim 8 wherein the cut-outis formed by laser cutting.
 10. The catheter of claim 8 wherein thecut-out is formed by etching.
 11. The catheter of claim 8 wherein thecut-out is a straight slit.
 12. The catheter of claim 8 wherein thecut-out is a curved slit.
 13. The catheter of claim 1 wherein theasymmetric film hinge is made of a different material that the firstsection of the strut and the second section of the strut.
 14. Thecatheter of claim 13 wherein the asymmetric film hinge is formed byattaching the first section of the at least one strut to the secondsection of the at least one strut.
 15. The catheter of claim 14 whereinthe first section of the at least one strut is attached to the secondsection of the at least one strut by welding.
 16. The catheter of claim15 wherein the first section of the at least one strut is attached tothe second section of the at least one strut by adhesive bonding.